1. Field of the Invention
The present invention relates to a bending apparatus for a long material such as round bars and pipes, and more particularly to technology which enables cold bending of the long material at an arbitrary bending radius without use of any special bending die for hot processing.
2. Description of the Related Art
As an apparatus for bending a long material such as a hollow bar and solid round bar, there is a CNC bender which executes cold bending. Generally, the CNC bender comprises a carriage for moving such a material in the longitudinal direction and positioning it by gripping a rear end thereof, a bending die in which a groove having a slightly larger bending radius than the material is formed in the outer periphery and a clamp having a groove similar to the bending die and holding the material in cooperation with the bending die. In this CNC bender, by moving the clamp along the outer periphery of the bending die, the material is drawn into the groove and bent. Next, the carriage is forwarded and by rotating the material as required, next bending operation is carried out.
Because in the aforementioned CNC bender, the bending radius of the material is determined by the bending radius of the bending die, the kinds of the bending radii are restricted. Further, because a head portion comprised of the bending die, the clamp and the like is large, a trace of a bent material may interfere with the head portion or other attached equipment, thereby possibly restricting a bending processing shape.
Because the CNC bender has the above-described restriction, hot-bending by use of a dedicated total bending die for each product is a main stream for, for example, a solid stabilizer. However, the dedicated total bending die is quite expensive and production cost is relatively high if a bending die is prepared for even a product having a small production amount. Further, because spare parts need to be supplied still even after production thereof is stopped, its special bending die needs to be stored for a long period, so that a large amount of space is required. Further, in case of producing a prototype which cannot be cold-processed with the CNC bender, a skilled worker corresponds to this demand by partially heating the material and manually bending it. Therefore, there is such a problem that due date required by a customer cannot be satisfied sufficiently.
Accordingly, an object of the present invention is to provide a bending apparatus for a long material capable of cold-bending material at an arbitrary curvature radius and bending angle without using any special bending die.
To achieve the above object, the present invention provides a bending apparatus for a long material comprising: supporting device for supporting a long material in cantilever fashion at least in a bending direction; bending device which nips the material at an input point apart from the supporting device and is rotated by a predetermined angle so as to bend the material between the supporting device and the input point; driving device for rotating the bending device; feeding device for moving the material toward the bending device and setting a position of the material; and moving device which sets up a separation distance between the supporting device and the bending device prior to bending of the material and allows the supporting device and the bending device to move relatively during the bending of the material.
The operation of the present invention will be described with reference to FIGS. 1, 2. If the bending device 2 is rotated by an angle xcfx86 at an input point B, a uniform moment is applied to the material W supported by the supporting device 1 between the input point B and a supporting point A, so that the material W is bent by the angle xcfx86 with a predetermined curvature radius. In this case, the curvature radius of the material W can be set up by setting a separation distance S between the input point B and the supporting point A appropriately. That is to say, according to the present invention, the material W can be bent at an arbitrary curvature radius and bending angle without using any special bending die. Further, by rotating the bending device in a direction opposite to that shown in FIG. 1, the material can be bent inversely, thereby making it possible to prevent an interference between the material W and the bending apparatus or other attached equipment.
After bending processing at one position is finished, the material W is fed toward the bending device by the feeding device and next bending is started. At this time, the moving device moves any one or both of the supporting device 1 and the bending device 2 so as to set up a separation distance S. FIG. 1 shows an example in which the supporting device is fixed on an apparatus main body while the moving device 3 moves the bending device. In this case, the moving device 3 is an arm which is movable in the lateral direction in the FIG. 1 with respect to the supporting device 1 and rotatable around an end portion opposite to the bending device 2.
FIG. 2 shows an example in which the bending device 2 is fixed on the apparatus main body while the moving device is capable of moving the supporting device 1. The moving device 3 is an arm which can approach or leave the bending device 2 and is rotated around an end portion opposite to the bending device 2. With such a structure, when the bending device 2 is rotated, the moving device 3 is moved following the bending of the material W.
In FIG. 1, the moving device 3 can be provided with driving device. For example, by disposing hydraulic cylinders on both sides of the moving device 3 and coupling a piston of the hydraulic cylinder to an outer periphery of the bending device 2 according to an appropriate method, reciprocating motion of the piston can be converted to a rotating motion of the bending device 2. Alternatively, it is permissible to provide the moving device 3 with a rotation driving mechanism such as a hydraulic motor and further provide this rotation driving mechanism with the bending device 2. However, in this case, a reaction force of moment applied to the bending device 2 is applied to a rotation center P of the moving device 3. Consequently, an additional moment is applied to the material W so that the bending radius is not uniform at respective points of the material. This additional moment in FIG. 1 is analyzed as follows.
Assume that a reaction force applied to the rotation center P of the moving device 3 in FIG. 3 is F and moment given to the material W by the bending device is Mw. This moment Mw is a moment acting equally on respective points of the material. About balance of moment around the point B, which is applied to the moving device in FIG. 3, the following formula is established.
F*L1=Mxe2x80x83xe2x80x83(1)
About balance of moment around the point B acting on the material, the following formula is established.
F*L2+Mw=Mxe2x80x83xe2x80x83(2)
Here, M in the formula indicates a decay moment inherent of the material and is provided schematically with the following formula.
M=d3*"sgr"/6xe2x80x83xe2x80x83(3)
d: material diameter
"sgr": stress at yield
According to the formula (2), moment of F*L2 as well as moment Mw by the bending device is applied to the material. If the length L1 of the moving device is set long, according to the formula (1), F decreases inversely proportionally. Thus, the term of F*L2 in the formula (2) decreases. Therefore, by prolonging the length of the moving device sufficiently, moment applied to the material is substantially equalized, thereby making the bending radius substantially uniform.
When the driving device for rotating the bending device 2 is separated dynamically from the moving device 3, F equals 0 in the formulas (1) and (2), and Mw equals M. That is, it is preferable since the moment in overall the bending area S is uniform. For example, in the example shown in FIG. 1, it is permissible to fix the driving device to the apparatus main body and couple the driving device with the bending device 2 by device of a joint such as universal joint. In contrast, when the example shown in FIG. 2 is dynamically analyzed, although the moment in overall the bending area S cannot be completely uniform, but can be approximately uniform by setting up the length L1 of the moving device sufficiently large. Therefore, in this case also, it is desirable to set up the length of the moving device sufficiently large.
Preferably, any one or both of the supporting device and the bending device has gripping device for gripping detachably the material with inner peripheral faces thereof having a configuration fitting to outer peripheral faces of the material. With such a structure, it is possible to suppress flattening or occurrence of pressure mark which may occur when the material is bent. Further, preferably, the feeding device includes rotating device for rotating the material around its axis in the longitudinal direction and setting an angular position. By rotating the material while feeding it, a three-dimensional product can be processed. Meanwhile, although the present invention is suitable for cold bending processing of a solid stabilizer, the present invention is not restricted to the manufacturing of such a product. Further, the material for use is not restricted to a round bar, but may be applied to material having an arbitrary cross section such as H-shaped channel and C-shape/L-shaped channel.